Description—Balsam of Tolu freshly imported is a light brown, slow-flowing resin, soft enough to be impressible with the finger, but viscid on the surface.[795] By keeping, it gradually hardens so as to be brittle in cold weather, but it is easily softened by the warmth of the hand. Thin layers show it to be quite transparent and of a yellowish brown hue. It has a very agreeable and delicate odour, suggestive of benzoin or vanilla, especially perceptible when the resin is warmed, or when its solution in spirit is allowed to evaporate on paper. Its taste is slightly aromatic with a barely perceptible acidity, though its alcoholic solution decidedly reddens litmus.
In very old specimens, such as those which during the last century reached Europe in little calabashes[796] of the size and shape of an orange, the balsam is brittle and pulverulent, and exhibits when broken a sparkling, crystalline surface. This old balsam is of a fine deep amber tint and superior fragrance.
When Balsam of Tolu is pressed between two warmed plates of glass so as to obtain it in a thin even layer, and then examined with a lens, it exhibits an abundance of crystals of cinnamic acid. Balsam of Tolu dissolves easily and completely in glacial acetic acid, acetone, alcohol, chloroform or solution of caustic potash; it is less soluble in ether, scarcely at all in volatile oils, and not in benzol or bisulphide of carbon. The solution in acetone is devoid of rotatory power in polarized light.
Chemical Composition—The balsam consists partly of an amorphous resin, not soluble in bisulphide of carbon, which is supposed to be the same as the dark resin precipitated by the bisulphide from balsam of Peru. Scharling (1856) assigned the formula C₁₈H₂₀O₅ to that part of the balsam which is soluble in potash.
If Tolu balsam is boiled with water, it yields to it cinnamic and benzoic acid, which we have (1877) perfectly succeeded in separating by repeated recrystallization from water; we have before us good specimens of either, showing not only different melting points (133° C. and 121° C.), but as to our crystals of benzoïc acid, isolated from the balsam as stated above, we find that they also do not evolve bitter almond oil when mixed with sulphuric acid and chromate of potassium. The acids may also be removed by boiling bisulphide of carbon.
Busse[797] showed that benzylic ethers of both benzoic and cinnamic acid are also constituents of the balsam, the cinnamate of benzyl being present in larger quantity.
Upon distilling the balsam with water, it affords 1 per cent. of Tolene, C₁₀H₁₆, boiling at about 170° C. This liquid rapidly absorbs oxygen from the air. By destructive distillation, the balsam affords the same substances as those obtainable from balsam of Peru, among which Phenol and Styrol have been observed.
Commerce—The balsam is exported from New Granada, packed in cylindrical tins holding about 10 lb. each. The quantity shipped from Santa Marta in 1870 was 2,002 lb.; in 1871, 2,183 lb.; in 1872, 1,206 lb. In 1876 from the port of Savanilla 27,180 kilogrammes are stated to have been exported.
Uses—Balsam of Tolu has no important medicinal properties. It is chiefly used as an ingredient in a pleasant-tasting syrup and in lozenges.
Adulteration—We have twice met with spurious Balsam of Tolu, but in neither instance did the fraudulent drug bear any great resemblance to the genuine.